Ships and other marine surface vessels, and particularly those which are unarmed or incapable of mounting a counter-attack, are particularly vulnerable to torpedo and surface missile attack by submarines, aircraft or surface warships. The only defensive measure the vessel being attacked may be able to take is randomly to change course, this commonly being referred to as zig-zagging. Such maneuver, however, is not extremely effective particularly in light of modern-day guided missiles and torpedoes which have the ability to change their course and home-in on the vessel. Accordingly, the vessel which may be vital to a nation's defense may be destroyed or seriously damaged.
Various attempts have been made to afford surface vessels a greater degree of protection against projectile attack. One such attempt, disclosed in U.S. Pat. No. 2,369,464, provides a torpedo intercepting apparatus comprising a series of articulated screens or elements. Each screen element includes a series of spaced vertical rods and longitudinal tie rods which extend above and below the surface of the water, and an articulated screen is towed at each side of the vessel by means of a boom secured to the bow of the vessel. To defense against an attack, propulsion devices at the lead ends of the screens cause the booms to pivot away from the vessel, thus to locate the screens in laterally spaced relationship with respect to the vessel. If a torpedo detonates upon striking a screen, the resultant explosion may be sufficiently spaced from the vessel to prevent serious damage. Alternatively, the torpedo causes the screen to rotate whereby the momentum of the torpedo is converted in part to a turning moment acting upon the screen and in part to a component tending to move the screen toward the vessel. It is noted, however, that an anticipated drawback of such apparatus is that a second trailing torpedo may be permitted to pass once a first torpedo has caused the screen to rotate to a horizontal position. Moreover, the vessel with such screens deployed would still be vulnerable to frontal and rear attack.
In U.S. Pat. No. 2,968,274, another type of anti-torpedo system can be seen to employ one or more flexible tubes or streamers which are towed by a vessel through the water at a predetermined depth of submergence and in predetermined laterally spaced relation with respect to the vessel. A plurality of microphonic detecting devices are arranged at intervals along respective streamers whereas explosive charges are disposed along the length of respective streamers, each explosive charge being of sufficient size to deflect, disable or destroy an oncoming torpedo as the charge is fired by a signal received through the water by the microphonic detecting devices. Perhaps the major drawback of this type of protection system is its complexity which may render it prone to failure. Moreover, such system may not be effective against projectiles traveling above the surface of the water.